Counter-current cycling extraction

ABSTRACT

A counter-current cycling extraction method wherein a light solvent upward stream extracts a solute from a heavy solvent downward stream, the improvement which comprises during the circulation of said light solvent upward stream simultaneously circulating an upward stream of the heavy solvent whose solute has been removed at least in part by extraction, the amount of said heavy solvent thus circulated corresponding substantially to the volume increase of the light solvent stream due to the solute transfer, thereby maintaining during the cycling extraction the volume of heavy solvent stream constant and generally enabling a constant volume flow of the light solvent stream and apparatus therefore, comprising a cycling extraction column provided with compensating means for feeding a controlled amount of solvent having reduced solute concentration into the base of said extraction column during the flow of the light solvent.

ilnited States Patent i et al.

COUNTER-CURRENT CYCLING- EXTRACTION Inventors: Chandrasekhara Rao Darsi, John Edwin Feick, Edmonton, Alberta; Isa Christopher Mustaklem, St. Albert, Alberta, all of Canada Chemcell Limited, Montreal, Quebec,Canada Filed: on. 6, 1969 Appl. No.: 863,879

Assignee:

US. Cl. ..260/541, 23/2705, 23/310 Int. Cl ..C07c 51/48 Field of Search ..23/310, 270.5; 260/541 References Cited UNITED STATES PATENTS 4 4/1953 Grunewald et al ..23/310 X 6/1956 Maycock et a]. ..23/310 10/1956 Maycock et a1. ..23/310 6/1966 Heinrich ..23/310 2/1966 Mcwhirter ..23/270.5

[ 51 Sept. 19,1972

Primary Examiner-Lorraine A. Weinberger Assistant Examiner-Richard D. Kelly AttorneyThomas J. Morgan and Marvin Turken [5 7] ABSTRACT A counter-current cycling extraction method wherein a light solvent upward stream extracts a solute from a heavy solvent downward stream, the improvement which comprises during the circulation of said light solvent upward stream simultaneously circulating an upward stream of the heavy solvent whose solute has 4 Claims, 1 Drawing PATENTEI] SEP 1 9 I972 HEAVY PHASE LIGHT PHASE LIGHT PHASE PRODUCT HEAVY PHASE PRODUCT INVENTORS Chundrosekhoro Ruo DARSI John Edwin FEICK lsu Christopher MUSTAKLEM PATENT AGENTS 1 COUNTER-CURRENT CYCLING EXTRACTION This invention relates to. a counter-current, cycling extraction method where the transfer of solute is from a heavy phase to a light phase and the apparatus therefore.

Counter-current extraction is generally accomplished by the simultaneous flow of two substantially immiscible streams, a heavy one comprising 'a heavy solvent and a light one comprising a light solvent, fonning two phases, one of said phases containing at least one solute to be transferred from one stream to the other. Such methods are used for the separation or extraction of the components of a solution.

To increase the efficiency and capacity of multi stage extraction columns, it has been found advantageous to cyclically control them. This can be effectively done when a solute is transferred from a light to a heavy stream by alternately flowing the heavy stream and the light stream. However, for the extraction of a solute from a heavy to a light stream using cyclic operation, the light phase takes up the solute and increases in volume and as a result the light phase accumulates at the bottom while the heavy phase accumulates at the top. In other words the column is flooded and stable operation becomes impossible.

Broadly stated, there has now been found in countercurrent cycling methods, wherein a light solvent upward stream extracts a solute from a heavy solvent downward stream, the improvement which comprises, during the circulation of said light solvent upward stream, simultaneously circulating an upward stream of the heavy solvent whose solute has been removed at least in part by extraction, the amount of said heavy solvent thus circulated corresponding substantially to the volume increase of the light solvent stream due to the solute transfer, thereby maintaining during the cycling extraction the volume of heavy solvent stream constant, and generally enabling a constant volume flow of the light solvent stream and an apparatus therefore. The amount of said heavy solvent is generally conveniently fed as a stream independent of said light stream but running parallel thereto.

In a particular embodiment, there has now been found a countercurrent cycling extraction method whereby a solute is transferred from a heavy solvent stream to a light solvent stream, the said two streams being substantially immiscible into one another, the process comprising alternatively pressuring down a stream of heavy solvent containing a solute into a zone and then pressuring up into said zone through said heavy solvent, a stream of light solvent to remove from said heavy solvent, said solute, and simultaneously collecting in alternate order from said zone, near the bottom an amount of heavy solvent stream having reduced solute concentration substantially corresponding to the amount of heavy solvent which is simultaneously fed, and during the light solvent flow collecting from the top of the zone a solute-enriched light stream, while feeding into said zone near the bottom and into the heavy solvent stream, an amount of said heavy solvent of reduced solute concentration corresponding substantially to the volume increase of the light solvent stream due to the solute transfer to maintain the volume of the heavy solvent stream constant throughout the extraction method.

ketone and an aqueous solution of acetic acid, as will be discussed in detail in the Examples.

There has also been found a cyclically-controlled extraction apparatus for the transfer of a solute from a stream comprising a heavy solvent, into a counter-current stream comprising alight solvent, wherein the said streams are substantially immiscible, the said apparatus comprising:

a. an extraction column provided with feeding means to pressure into said column respectively, a

downward stream of a heavy solvent containing a solute, and an upward stream of a light solvent;

b. outlet means to take out respectively, the light stream containing solute, and the heavy solvent stream having reduced solute concentration;

c. means co-operating with said feeding means and said outlet, means for cyclically opening and closing said heavy solvent feeding means and outlet, while cyclically closing and opening said light solvent feeding means and outlet;

d. compensating means for feeding a controlled amount of the solvent having reduced solute concentration into the base of said extraction column during the flow of the light solvent.

Having thus generally described the invention, it will now be referred to in more details by reference to the accompanying drawing which is a schematic drawing of an extraction column cyclically controlled for carrying out particular embodiments of the invention wherein the continuous line represents the process line; the segmented lines, pneumatic lines; and the dot-dash lines, electrical lines.

Referring now to the drawing, 10 designates an extraction column, partially shown in exploded view, and having enlarged ends to promote settleing, and in which some of the perforated plates, such as sieve trays l2, l3 and 14, may be seen defining stages with the walls of column 10. Preferably the perforations of these plates should be small so as to affect efficient contact. Other contacting means, such as packing, may be added if desired. A light phase is introduced into the lower portion of the column 10 via line 16 and a heavy phase into the upper portion of the column 10 via line 18. The driving forces to enable the flow of said phases into two streams in the extractor 10, are gravity and pressure. This latter force (pressure) is described at greater length herein below. In between a pair of adjacent perforated plates, the interface between the light and the heavy phase may be seen; for instance, at 19 or 20. Once the light phase reaches the overhead of extractor, itescapes via line 21 and may be collected by any means; for instance, it may be kept in a reservoir 22; while the heavy phase escapes at the bottom of the column via line 24. The line 21 is also provided with a vent 23 for the escape of gases and safety purposes. Line 18 ends below 21, and line 16 above 24 to in- II'AIAQA MAI:

troduce the heavystream below the interface of the last stage and the light stream above the interface in the first stage, to minimize the turbulence created by the incoming streams so that the two immiscible streams be well separated as they leave the extraction column.

Pressure, The Second Driving Force tank 41 via line 42 into line 18. Lines 16 and 18 are also provided, respectively, with valves 34 and 44, and flowmeasuring devices 33 and 43. The flow in line 16 actuates the flow measurement device 33 which, in turn, feeds a signal into a flow-regulating control 35 via a transmitter 36. The flow-regulating control 35 controls the valve 34 to maintain the required flow in line 16 by means of the pneumatic line 37. The same is to be said for flow-regulating control 45 pneumatically actuating valve 44 according to the signal received from the flow measuring device 43 via the transmitter 46. The on-off solenoid valves 38 and 48 are actuated cyclically by a cycletimer 50 which generates electrical signals along lines 35 and 45 to 38 and 48 for pneumatically closing and opening in alternate order, valves 34 and 44 so that one phase forming a stream is flowing at a time. In particular embodiment, this flow at each cycle of each stream takes the form of alternating square waves or approximations of them.

Near the bottom of the extraction column 10, line 24 is provided with a pump 60 to remove the heavy solvent stream having reduced solute concentration and feed into a reservoir 61 via line 62. The overflow of heavy solvent in 61 may be kept in a storage tank 63 or delivered where necessary. Line 62 is provided with an onoff valve 58 operated by the electrical signals generated from line 45 by the cycle timer 50 so that valves 64 and 44 be both opened at the same time.

To maintain the level of the original phase constant inside the extractor, a level control 65 pneumatically regulates via 64 the flow of heavy stream in line 24.

A Recycling Stream A circulating pump 67 recycles the depleted heavy phase in reservoir 61 via line 70 into the bottom of the extraction column 10. The line 70 is also provided with valves 68 and 72, the latter being activated by the cycle timer 50 by line 35 so that both valves 72 and 34 by opened at the same time. The flow through valve 72 is also controlled by a flow controlling device as previously described.

Theoretical Consideration Involving the Transfer of Solute From Heavy to Light Phase The flow of the phases in extraction columns is due to pressure and gravity. If a certain amount of heavy phase is introduced near the top of the column and the light phase line shutoff, the heavy liquid will reach the bottom of the column, given enough time. If the light phase is flowing up the column simultaneously, the flow of heavy phase down the column can generally be stopped, given a high enough flow rate of the light phase; this is also known as flooding. Flooding is to be avoided as it disrupts the aims of such apparatus. In a controlled cycling extractor, only one phase is flowing at a time. During the light phase flow period, a certain amount of pure, light solvent is introduced into the bottom section of an extraction column. The liquid mixes with the mixture of heavy solvent and solute present in that stage and some of the solute is dissolved into the light phase, and its volume increases as a result. The volume of liquid leaving this stage to the nexthigher one is equal (in this short period of flow) to the volume introduced, and hence there is a net gain of light phase in the bottom of the extraction column. The process occurs in all the consecutive stages and the volume of light phase leaving as an overflow at the top of the column is equal to the amount introduced. The gain on the light phase volume by virtue of solute transfer remains in the column.

During the heavy phase flow period, a mixture of heavy solvent and solute is introduced at the top of the column, mixes with the light phase and some transfer of solute to the light phase occurs. The mode of operation is by drawing heavy phase out at the base. In an ideal situation, the amount of base product that should be necessary to draw at the bottom is the volume of heavy phase that would reach the base after going through transfers at various stages. This means that successively less amounts of heavy phase must pass through successive stages. Since the bulk flow through the column is governed by what is drawn off at the bottom, the excess amount (which is equal to the volume of the solute) introduced at the top will stay at the top of the column.

In this manner, during successive light phase flow cycles, more and more of light phase will accumulate at the bottom section and during heavy phase flow cycles more and more of heavy phase will accumulate at the top, creating a pseudo flooding condition. Total amount entering is not equal to total amount leaving; after a few cycles, the excess amount of heavy phase will find its way out of the column via overhead lines. Such a situation will result regardless of the rates.

The Present Process To remedy this situation without its effecting the operating characteristics, during the heavy phase flow period, an amount of the heavy phase at the bottomof the zone equal in volume to the amount introduced at the top is deliberately drawn out. This operation, if performed without a corrective action at a later stage, will deplete the column of heavy phase. By this operation, the flow of heavy phase down the column is aided and the accumulation of it at the top is thus avoided and all the transfer that is supposed to occur will happen. It is to be noted that the amounts of heavy phase leaving successive stages is less; hence a slight amount of light phase is brought down to the next lower stage and so on.

The difficulty encountered in forcing more light phase up the column than the amount introduced at the bottom is taken care of during the light phase flow I n i A Min increase in the light phase due to solute transfer. The light phase introduced forces an equal volume of light phase through the successive higher stages; in addition, the heavy phase recycle introduced will force an equal volume of light phase up the column which also is the amount of light phase that would be formed during its travel up the column.

In summary then, for the operation of a controlled cyclic (CC) extractor when solute is being transferred from heavy to light phase, an amount of base product equal to the volume increase in the light phase due to solute transfer is introduced at the base of the column during the light phase flow period which pushes the required amount of light phase up through successive EXAMPLES l-5 A heavy phase downwardly directed, and a countercurrent light phase, are cyclically fed under pressure into an apparatus as shown in the drawing, during about l0-cycles. The heavy phase contains an aqueous solution of about percent by weight of acetic acid, the solute. The light phase is methyl-isobutyl ketone.

During the extraction process the acetic acid concentration of each entering and leaving stream is recorded.

The results thus obtained are shown in Table l. The

total throughput of both streams in US gallons per hour per ft. is shown in the first column.

TAB LE 1 the column is greatly enhanced during cyclic operation and comparisons may be made with conventional operations showing efficiencies at least 100 percent greater and a capacity increase of at least percent over the flooding point for this system.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a counter-current cycling extraction method wherein a light solvent upward stream extracts a solute from a heavy solvent downward stream, the said two solvent streams being substantially immiscible in one another, the improvement which comprises during the circulation of said light solvent upward stream simultaneously circulating an upward stream of the heavy solvent whose solute has been removed at least in part by extraction, the amount of said heavy solvent thus circulated corresponding substantially to the volume increase of the light solvent stream due to the solute transfer, thereby maintaining during the cycling extraction the volume of heavy solvent stream constant and generally enabling a constant volume flow of the light 91Ysnt$E em-,,. 2. A counter-current cycling extraction method whereby a solute is transferred from a heavy solvent stream to a light solvent stream, the said two streams being substantially immiscible into one another, the process comprising alternatively pressuring down a stream of heavy solvent containing a solute into a zone and then pressuring up into said zone and through said heavy solvent, a stream of light solvent to remove from said heavy solvent said solute, and simultaneously collecting, in alternate order from said zone near the bottom, an amount of heavy solvent stream having reduced solute concentration substantially corresponding to the amount of heavy solvent which is simultanet s xfa ta lsl7dwinslha blsalysm fl stias Discussion It can be easily seen from Table I that efficiency of Acetic acid conc. (weight percent) Volum Total flow Light phase Heavy phase throughratio Effiput, USG/ heavy] Entering Leaving Entering Leaving ciency, No. hit/it. light (at 16) (at (at 18) (at 24) percent Example: v

1 44s 0. 95 o. 16 13.06 19. 72 1. 20 as. 4 0. so 0. 31 1s. 50 20.11 5. 66 as. 2 0. 9s 0. 51 13. 33 1s. 96 1. s4 s7. 5 0.88 0. 30 13. 7e 20. 22 6.30 41. 4 0.86 o. 25 13. 0s 1s. 82 5. 71 47. o

0. 91 24. e 5. 12. 0. 0 15. 4 24. s 0. 95 24. 4 5. 7O 0. 0 15. 0 21. 1

Sample A from the top of the zone a solute enriched light stream, 55 while feeding into said zone near the bottom and into ste i s gggg ggg gi gz gg the heavy solvent stream an amount of said heavy solb 6 eye 2, 3 3 :9 Op tin n at the base and the vent whose solute has been removed at least in part by g i g ig f gg gg ggr g e extraction, said amount of heavy solvent corresponding p substantially to the volume increase of the light solvent Samples B and C stream due to the solute transfer to maintain the volume of the heavy solvent stream constant The same is repeated except that the solute lS disthroughout the extraction method Solved the light P instead of heavy Phase 3. The method according to claim 2 wherein the said that the streams are continuously fed instead of cychzone contains aplurality of stages cally. The results are also shown in Table l. The method according to claim I wherein the heavy solvent containing a solute is an aqueous solution of acetic acid, and the light solvent stream is methylisobutyl ketone. 

2. A counter-current cycling extraction method whereby a solute is transferred from a heavy solvent stream to a light solvent stream, the said two streams being substantially immiscible into one another, the process comprising alternatively pressuring down a stream of heavy solvent containing a solute into a zone and then pressuring up into said zone and through said heavy solvent, a stream of light solvent to remove from said heavy solvent said solute, and simultaneously collecting, in alternate order from said zone near the bottom, an amount of heavy solvent stream having reduced solute concentration substantially corresponding to the amount of heavy solvent which is simultaneously fed, and during the light solvent flow collecting from the top of the zone a solute enriched light stream, while feeding into said zone near the bottom and into the heavy solvent stream an amount of said heavy solvent whose solute has been removed at least in part by extraction, said amount of heavy solvent corresponding substantially to the volume increase of the light solvent stream due to the solute transfer to maintain the volume of the heavy solvent stream constant throughout the extraction method.
 3. The method according to claim 2 wherein the said zone contains a plurality of stages.
 4. The method according to claim 1 wherein the heavy solvent containing a solute is an aqueous solution of acetic acid, and the light solvent stream is methyl-isobutyl ketone. 